When potato plants bloom, they send up five-lobed flowers that spangle fields like fat purple stars. By some accounts, Marie Antoinette liked the blossoms so much that she put them in her hair. Her husband, Louis XVI, put one in his buttonhole, inspiring a brief vogue in which the French aristocracy swanned around with potato plants on their clothes. The flowers were part of an attempt to persuade French farmers to plant and French diners to eat this strange new species. Today the potato is the fifth most important crop worldwide, after wheat, corn, rice and sugar cane. But in the 18th century the tuber was a startling novelty, frightening to some, bewildering to others—part of a global ecological convulsion set off by Christopher Columbus.
About 250 million years ago, the world consisted of a single giant landmass now known as Pangaea. Geological forces broke Pangaea apart, creating the continents and hemispheres familiar today. Over the eons, the separate corners of the earth developed wildly different suites of plants and animals. Columbus’ voyages reknit the seams of Pangaea, to borrow a phrase from Alfred W. Crosby, the historian who first described this process. In what Crosby called the Columbian Exchange, the world’s long-separate ecosystems abruptly collided and mixed in a biological bedlam that underlies much of the history we learn in school. The potato flower in Louis XVI’s buttonhole, a species that had crossed the Atlantic from Peru, was both an emblem of the Columbian Exchange and one of its most important aspects.